What are the contraindications for Viagra (sildenafil) in adult males with erectile dysfunction?

Contraindications for Viagra (Sildenafil)

The absolute contraindication for Viagra is concurrent use of nitrates in any form—including oral, sublingual, transdermal, or recreational "poppers"—due to the risk of potentially fatal hypotension. 1, 2

Absolute Contraindications

Nitrate Use (Any Form)

• Organic nitrates are absolutely contraindicated with sildenafil, whether used regularly or intermittently. 1, 2
• This includes:
  • Nitroglycerin (tablets, patches, sprays, ointments) 2
  • Isosorbide mononitrate or dinitrate 1, 2
  • Recreational "poppers" (amyl nitrate or nitrite) 3, 2
• The combination can cause dangerous, life-threatening hypotension due to potentiation of blood pressure drops. 2, 4, 5

Known Hypersensitivity

• Sildenafil is contraindicated in patients with known hypersensitivity to sildenafil or any tablet component. 2
• Hypersensitivity reactions reported include anaphylaxis, anaphylactic shock, and anaphylactoid reactions. 2

Critical Safety Considerations Before Prescribing

Cardiovascular Risk Assessment

• Patients whose cardiovascular risk is indeterminate or who cannot perform moderate physical activity (3-5 METs) should be referred to cardiology before prescribing sildenafil. 3, 6
• Sildenafil is generally safe in low-risk cardiovascular patients, including those with:
  • Asymptomatic coronary artery disease with <3 risk factors 6
  • Controlled hypertension 6
  • Mild, stable angina 6
  • Successful coronary revascularization 6
  • Uncomplicated past myocardial infarction 6
  • Mild valvular disease 6
  • CHF (NYHA class I) 6

Relative Contraindications and Cautions

• Use caution within 6 months of acute myocardial infarction or stroke. 7
• Inadvisable in patients with unstable angina pectoris. 7
• Use caution in cardiac failure. 7
• Uncontrolled hypertension is a relative contraindication. 7
• Impaired cardiac reserve requires caution. 7

Emergency Nitrate Protocol

If a patient on sildenafil requires emergency nitrate administration, wait 24 hours after sildenafil before giving nitrates, under close medical supervision with continuous patient monitoring. 6

Drug Interactions Requiring Dose Adjustment

CYP3A4 Inhibitors

• Potent CYP3A4 inhibitors significantly increase sildenafil levels and require dose adjustment to 25 mg: 8, 4
  • Ritonavir 4
  • Saquinavir 4
  • Ketoconazole 8, 4
  • Erythromycin 4
  • Cimetidine 4

Cannabis/THC Use

• Explicitly ask about cannabis use, as THC inhibits CYP3A4 and may increase sildenafil plasma concentrations, potentially enhancing vasodilatory effects and cardiovascular risk. 8

Special Populations Requiring Dose Reduction

• Elderly patients: Start with 25 mg. 4
• Hepatic impairment: Start with 25 mg; severe hepatic impairment generally not recommended. 6, 4
• Renal impairment: Start with 25 mg. 4

Common Pitfalls to Avoid

• Always explicitly ask about ALL forms of nitrate use, including recreational "poppers," before prescribing. 3, 2
• Do not prescribe without assessing baseline cardiovascular risk and ability to perform moderate physical activity. 3, 6
• Do not combine with other PDE5 inhibitors—patients should not take sildenafil 25/50/100 mg for ED if already on sildenafil 20 mg for pulmonary hypertension. 2
• Heavy alcohol use should be avoided as it impairs erectile function and increases adverse effect risk. 6